1. Field of the Invention
The present invention relates to drive devices and, more particularly, to a drive device including both a first drive means, containing a working fluid and operated in response to a change in volume of the working fluid, and a second drive means connected to the first drive means and controlling inflow and outflow of the working fluid relative to the first drive means.
2. Description of the Prior Art
The present invention, relating to a drive device, will be described in detail in conjunction with a drainage control device for washing machines, as an example.
As shown in FIG. 1, a conventional washing machine includes a drive motor 3. This motor 3 is installed within the lower chamber of the washing machine's cabinet at a position below a washing tub 1, and generates drive force for the tub 1. A power transmission unit 2 connects the drive motor 3 to the washing tub 1, and transmits the drive force of the motor 3 to the tub 1. A drain port 4a is provided on the bottom of the washing tub 1 at a position spaced apart from the power transmission unit 2. A drain hose 4 extends from the drain port 4a to the outside of the cabinet. The washing machine also has a drainage control device used for controlling the drain port 4a to discharge water from the washing tub 1, in addition to controlling the power transmitting operation of the power transmission unit 2. This drainage control device comprises a drain motor 5. This drain motor 5 is installed at a predetermined position spaced apart from both the power transmission unit 2 and the drain port 4a, and generates drive force for controlling the operation of both the drain port 4a and the power transmission unit 2.
A connection bracket 6, with a steel wire 6a, connects the drain port 4a to the drain motor 5. A brake lever (not shown) is connected to a connection lever 7 of the power transmission unit 2, and so the power transmission unit 2 is operated in conjunction with the drain motor 5. Therefore, both the power transmission unit 2 and the drain port 4a are operable in conjunction with the drain motor 5. When the brake lever is actuated in response to a rotation of the drain motor 5, the connection bracket 6 is pulled to open the drain port 4a. 
When the washing machine is turned on, water is fed into the washing tub 1 to reach a predetermined water level. When water reaches the predetermined water level within the washing tub 1, the pulsator of the tub 1 is rotated in opposite directions by the drive motor 3 to perform a washing mode. After the washing mode is finished, the drain motor 5 is activated to open the drain port 4a while controlling the operation of the power transmission unit 2, thus draining water from the washing tub 2 to the outside of the cabinet through the drain hose 4.
However, the drainage control device of the conventional washing machine has the following problems. That is, it is necessary for the drainage control device to include a drain motor 5 having a high power capable of pulling the connection bracket 6 to open the drain port 4a and pulling the connection lever 7 of the power transmission unit 2 to release a brake band (not shown) during a draining mode or a dehydrating mode. This drain motor 5 is fabricated with numerous gears 5a encased in a motor housing as shown in FIG. 2, and so the motor 5 has a complex construction and undesirably generates operational noise during an operation of the washing machine.
In addition, the gears 5a of the drain motor 5 are abraded through long periods of operation to cause operational errors of the motor 5. In the case of operational errors of the motor 5 due to an abrasion of the gears 5a, it is almost impossible to selectively replace abraded gears 5a with new ones. Accordingly, a user of the washing machine is forced to replace the motor 5 with a new one while paying excessive costs for the replacement. Due to the complex construction and the excessive number of gears 5a, the drain motor 5 undesirably increases the manufacturing and assembly cost of the washing machine.